Since I "bed" most of my rifles' actions and float the barrels, I find that as I approach the "sweet spot" as concerns the amount of powder used, the groups start to shrink.
At that point, I begin using incremental powder increases of only one tenth of a grain in the amount of powder I'm using and maintain the 1/10th of a grain incremental increase in powder until the groups begin to "open up" again which indicates that I've gone out the "top" of the "sweet spot".
As an example, my heavy-barreled Sako .222's "sweet spot" with VihtaVouri N130 powder is from 21.5 to 21.8 grains (inclusive) behind a 50 grain Sierra "Blitz" varmint bullet. At 21.9 grains, the MV increased, but the 5-shot groups began to open up again.
My Ruger #1 International's (aka "RSI") "sweet spot" with H4350 powder is from 47.2 grains to 47.6 grains (inclusive) behind a 140 grain Sierra flat-based ProHunter bullet.
When I actually get INTO the rifle's "sweet spot" which may be as little as a few tenths of a grain wide or as much as a half a grain wide, the 5-shot groups quickly get down to "minimum" size and stay there as the velocity increases with each new incremental increase in powder. Then, when just another 1/10th of a grain of powder is added, the group size begins to get larger... and groups get larger & larger as more and more powder is added.
Of course, all of this "accuracy" depends on the shooter being consistent and using good shooting techniques, the rifle being accurate shot-to-shot, the rifle rest being solid and the wind being consistent. Sometimes, this is a VERY hard combination to achieve and keep.
In testing and achieving s rifle's ultimate accuracy, "
consistency" in
ALL things is "king".
Strength & Honor...
Ron T.